OCR Configuration for Advanced Reading

TesseractConfiguration Properties

The TesseractConfiguration class provides the following properties for customizing OCR behavior. These are set through IronTesseract.Configuration.

Even with these high-level properties, IronOCR offers detailed customization through the TesseractVariables dictionary, which exposes hundreds of underlying Tesseract engine parameters for specialized use cases.

Setting Up a Character Whitelist for License Plates

A common use case for WhiteListCharacters is restricting OCR output to only the characters that can appear on a license plate: uppercase letters, digits, hyphens, and spaces. This eliminates noise and improves accuracy by telling the engine to ignore anything outside the expected character set.

Input

The following vehicle registration record contains a mix of uppercase text, lowercase text, special symbols (@, $, #, |, ~, ^, *), and punctuation. Only uppercase letters, digits, hyphens, and spaces should survive the whitelist.

:path=/static-assets/ocr/content-code-examples/how-to/ocr-configurations-for-advanced-reading.cs

using IronOcr;

// Initialize the Tesseract OCR engine
IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    // Whitelist only characters that appear on license plates
    WhiteListCharacters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789- ",

    // Blacklist common noise characters
    BlackListCharacters = "`~@#$%&*",
};

var ocrInput = new OcrInput();
// Load the input image
ocrInput.LoadImage("advanced-input.png");
// Perform OCR on the input image with ReadPhoto method
var results = ocr.ReadPhoto(ocrInput);

// Print the filtered text result to the console
Console.WriteLine(results.Text);

Output

The whitelist filtering is clearly visible in the results:

• "Plate: ABC-1234" becomes "P ABC-1234". The lowercase word "late:" is dropped, while the plate number is preserved exactly.
• "VIN: 1HGBH41JXMN109186" becomes "VIN 1HGBH41JXMN109186". The colon is dropped, but the uppercase VIN and full number are kept.
• "Owner: john.doe@email.com" becomes "O". The entire lowercase email and punctuation are removed.
• "Region: CA-90210 | Zone #5" becomes "R CA-90210 Z 5". The pipe (|) and hash (#) are removed, while the uppercase letters and numbers survive.
• "Fee: $125.00 + tax*" becomes "F 12500". The dollar sign, decimal point, plus sign, and lowercase "tax" are all removed.
• "Ref: ~record_v2^final" becomes "R 2". The tilde (~), underscore, caret (^), and all lowercase characters are stripped.

Configuring Barcode and Data Table Reading

IronOCR can detect barcodes and structured tables within documents alongside text. These features are controlled through TesseractConfiguration:

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    // Enable barcode detection within documents
    ReadBarCodes = true,

    // Enable table structure detection
    ReadDataTables = true,
};

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    // Enable barcode detection within documents
    ReadBarCodes = true,

    // Enable table structure detection
    ReadDataTables = true,
};

• ReadBarCodes: When set to true, IronOCR scans the document for barcodes in addition to text. Set to false to skip barcode detection and speed up processing when barcodes are not expected.
• ReadDataTables: When set to true, Tesseract attempts to detect and preserve table structures in the document. This is useful for invoices, reports, and other tabular documents.

These options can be combined with WhiteListCharacters and BlackListCharacters for precise control over what is extracted from complex documents.

Controlling Page Segmentation Mode

PageSegmentationMode tells Tesseract how to interpret the layout of the input image before recognizing text. Choosing the right mode for your document type has a direct impact on accuracy.

For a label or banner that contains a single line, SingleLine eliminates multi-block analysis and improves both speed and precision:

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    PageSegmentationMode = TesseractPageSegmentationMode.SingleLine,
};

using OcrInput input = new OcrInput();
input.LoadImage("single-line-label.png");

OcrResult result = ocr.Read(input);
Console.WriteLine(result.Text);

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    PageSegmentationMode = TesseractPageSegmentationMode.SingleLine,
};

using OcrInput input = new OcrInput();
input.LoadImage("single-line-label.png");

OcrResult result = ocr.Read(input);
Console.WriteLine(result.Text);

For a scanned page with irregular text placement (such as a receipt with scattered prices), SparseText recovers more content than Auto:

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    PageSegmentationMode = TesseractPageSegmentationMode.SparseText,
};

using OcrInput input = new OcrInput();
input.LoadImage("receipt-scan.png");

OcrResult result = ocr.Read(input);
Console.WriteLine(result.Text);

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    PageSegmentationMode = TesseractPageSegmentationMode.SparseText,
};

using OcrInput input = new OcrInput();
input.LoadImage("receipt-scan.png");

OcrResult result = ocr.Read(input);
Console.WriteLine(result.Text);

Generating Searchable PDFs and hOCR Output

RenderSearchablePdf and RenderHocr control the output formats that IronOCR produces alongside the plain text result.

RenderSearchablePdf embeds an invisible text layer over the original image, producing a PDF where users can search and copy text while the scanned image remains visible. This is the standard output format for document archival workflows.

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    RenderSearchablePdf = true,
};

using OcrInput input = new OcrInput();
input.LoadPdf("scanned-document.pdf");

OcrResult result = ocr.Read(input);
result.SaveAsSearchablePdf("searchable-output.pdf");

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    RenderSearchablePdf = true,
};

using OcrInput input = new OcrInput();
input.LoadPdf("scanned-document.pdf");

OcrResult result = ocr.Read(input);
result.SaveAsSearchablePdf("searchable-output.pdf");

RenderHocr produces an hOCR document, an HTML file that encodes the text content together with bounding box coordinates for every word. This is useful when downstream tools need precise word positioning (for example, redaction engines or document layout analysis).

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    RenderHocr = true,
};

using OcrInput input = new OcrInput();
input.LoadImage("document-page.png");

OcrResult result = ocr.Read(input);
result.SaveAsHocrFile("output.html");

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    RenderHocr = true,
};

using OcrInput input = new OcrInput();
input.LoadImage("document-page.png");

OcrResult result = ocr.Read(input);
result.SaveAsHocrFile("output.html");

Both flags can be enabled at the same time if you need all three output formats (plain text, searchable PDF, and hOCR) from a single read call.

Unicode Character Filtering for International Documents

For international documents in Chinese, Japanese, or Korean, the WhiteListCharacters and BlackListCharacters properties work with Unicode characters. This allows you to restrict output to specific scripts, such as only Hiragana and Katakana for Japanese.

Input

:path=/static-assets/ocr/content-code-examples/how-to/ocr-configurations-for-advanced-reading-jp.cs

using IronOcr;
using System.IO;

IronTesseract ocr = new IronTesseract();

ocr.Configuration = new TesseractConfiguration
{
    // Whitelist only Hiragana, Katakana, numbers, and common Japanese punctuation
    WhiteListCharacters = "あいうえおかきくけこさしすせそたちつてとなにぬねのはひふへほまみむめもやゆよらりるれろわをん" +
                            "アイウエオカキクケコサシスセソタチツテトナニヌネノハヒフヘホマミムメモヤユヨラリルレロワヲン" +
                            "0123456789、。？！（）¥ー",

    // Blacklist common noise/symbols you want to ignore
    BlackListCharacters = "★■§",
};

var ocrInput = new OcrInput();

// Load Japanese input image
ocrInput.LoadImage("jp.png");

// Perform OCR on the input image with ReadPhoto method
var results = ocr.ReadPhoto(ocrInput);

// Write the text result directly to a file named "output.txt"
File.WriteAllText("output.txt", results.Text);

// You can add this line to confirm the file was saved:
Console.WriteLine("OCR results saved to output.txt");

Output

Here's the output for the input above.

Because the whitelist includes only base Hiragana and Katakana characters, derived characters such as プ (pu) and デ (de) are dropped. Kanji, the Yen symbol, and full-width parentheses are also excluded since they are not in the whitelist. Blacklisted symbols like ★ and ■ are actively removed.

Conclusion

The TesseractConfiguration class gives developers fine-grained control over how IronOCR processes documents in advanced reading scenarios. By combining character whitelists with barcode detection, table reading, and international language support, you can build OCR pipelines tailored to specific document types such as license plates, passports, invoices, and multilingual content.

For more on the advanced reading methods themselves, see the ReadPassport guide, the ReadLicensePlate guide, and the full list of Tesseract configuration variables.